US2033481A - Paper manufacture - Google Patents

Description

Patented Mar. 10, 1936 I UNITED STATES PATENT OFFICE PAPER MANUFACTURE George A. Richter, Berlin, N. H., assignor to Brown Company, Berlin, N. IL, a corporation of Maine No Drawing. Application November 15, 1933,

' Serial No. 698,126

6. Claims. (01. 91-68) It has been proposed to introduce viscose into colored and give rise to odoriferous sulphur compaper for the purpose of imparting thereto varipounds when cellulose is regenerated therefrom, ous desirable qualities, for instance, high wet cellulose ether solutions are water white and strength, high wet strength coupled with high yield, when treated with suitable precipitants,

water absorbency, and high wet strength coupled the colorless cellulose ether unaccompanied by 5 with low water absorbency. The use of viscose obnoxious or odor-emitting compounds. as a paper-making ingredient, however, gives rise The solution of cellulose ether used in accordto various troubles. Thus, one serious trouble is ance with my invention in treating paper at any the impartation of foul odor to the paper. Anstage of paper manufacture may be one of the other serious trouble arising in the case of white desired caustic soda and cellulose concentration. 0 paper is the discoloration of the paper. Ac- In this connection, it is to be observed that after cordingly, a marketable paper containing viscose cellulose has been etherified in the presence of a as a paper-making ingredient is had only when suitable catalyzer with ethylene oxide to produce the viscose-treated paper is put through suitable the hydroxy ethyl ether of cellulose the ether after-treatments, all such papers requiring a may be dissolved in a caustic soda solution of 15 suitable deodorizing treatment and white paper 7% to 8% strength to form a solution of about requiring a suitable bleaching treatment. 8% cellulose ether content. The viscosity of such After extensive research work with a view toa solution is fairly high, but it may bereduced ward replacing viscose by a more satisfactory as by heating the solution somewhat or by dilutpaper-making ingredient, I have found that the ing the solution with water of suflicient causticity 20 cellulose ethers and more particularly the hyto keep the ether from precipitating. Once the droxy ethers of cellulose can be incorporated into solution of the ether has been incorporated at paper so as to impart thereto the desirable qualithe desired concentration and in the desired ties reached through the use of viscose but withamount into the paper-making stock or into the out encountering the drawbacks incident to the paper, the ether may be precipitated from solu- 25 use ofviscose. While various alkyl radicals like tion by neutralizing the alkali content of the somethyl, ethyl, propyl, butyl, etc., may enter into lution as with a suitable acid or acid salt solution, the formula of the hydroxy ethers of cellulose for instance, a solution of sodium bisulphate, used in accordance with my invention, I shall alum, etc., that does not decompose the ether ithereinafter speak more specifically about the hyself. The paper containing the precipitated cel- 30 droxy ethyl ether of cellulose not only because lulose ether may be glycerinatedjsoaped, or oththis ether can be prepared economically from erwise treated to acquire enhanced softness, pliethylene oxide and cellulose as raw materials, but ancy, and smoothness. because I have found it to be eminently satisfac- The incorporation of the cellulose ether into tory for the purpose of my invention. Inasmuch the paper may be effected by adding the solution 35 as the mode of preparation of this ether is now of ether to the paper-making stock and preknown and does not constitute part of the prescipitating the ether on the stock before it is deent invention, I need not dwell thereupon. Suflivered to the paper-making machine. In most flee it to say that the ether can be dissolved in a instances, however, it is preferable and more excaustic soda solution and that the resulting solupedient to treat a pre-fabricated paper sheet tion is sufliciently stable to be kept for a compara with a solution of the ether and with a precipitively long period of time without coagulating or tating reagent, particularly as such practice gelling. leads to a finished sheet wherein theprecipitated I have found that when the cellulose ether socellulose ether phase has a greater degree of con-,

lution is incorporated into-paper or into papertinuity. Assuming that one starts with a premaking stock and the ether precipitated out of fabricated sheet of paper, it is comparatively easy solution, it is possible to arrive at papers v of to treat the sheet with the cellulose ether soluhigh wet strength and otherwise simulating pation in various ways, for instance, by depositing pers treated with viscose. As already indicated, the ether solution as a coating on either or both papers so impregnated with cellulose ether posfaces of the sheet through the use of kissing 50 sess the important advantage over viscose-treated rolls or other coating instrumentalities, by passing papers that they are free from odoriferous or colthe sheet through a bath of ether solution and oring contaminations and hence require no after then squeezing the impregnated sheet to the treatments. Those skilled in the art will appredesired solution content, or by spraying the ether ciate the fact that whereas viscosesolutions are solution on either orboth faces of the sheet.

After treatment with the ether solution the paper may be treated in wet or partially dried conditlon with a suitable precipitant applied as in the form of an aqueous solution of acid or acid salt, as hereinbefore described, or in the form of a suitable acid gas or vapor, such as moist sulphur dioxide. The resulting paper contains not only the pricipitated ether, but also the sodium salt of the acid used as the precipitant. If desired, the salt may be leached out of the paper in a bath of water, preferably hot, but this is not necessary since the salt does not detract appreciably from the qualities sought in the finished paper. It is, of course, possible to perform the treatments of the present invention upon the paper while the paper is pursuing its usual course on the paper-making machine, for instance, while it is traversing the wet end of the paper machine or as it is being delivered from the dry end of the paper-making machine. In some instances, however, the'dry paper may be rolled up or accumulated, progressively withdrawn from the roll and put through the treatment with cellulose ether solution, the treatment with precipitant, and, if desired, the treatment with wash water; or the paper may be accumulated after each of these treatments.

The principles of the present invention may be applied in producing papers of various characteristics, for instance, a dense paper made from well beaten paper-making stock and/or body-sized with rosin, wax, or the like, may be coated with a comparatively thick or viscous solution of the ether which remains essentially only on the surface of the paper so that when the coated paper is treated with a suitable precipitant for the ether solution, a film or skin of ether is formed on the surface of the paper. In another instance, a thick solution of the ether may be squeezed or otherwise forced into an absorbent paper in amount sufficient to occupy so much of the pores and voids in the paper as to leave the paper quite unabsorbent once the ether has been precipitated in situ in the pores or voids. Both the foregoing results may be had by starting with the proper kind of paper base and/or by using a cellulose ether solution of comparatively high cellulose ether content, say, about 8%.

A most important sphere of application of my invention is, however, the manufacture of porous and absorptive paper of high wet strength containing an amount of cellulose ether distributed therethrough such as will not detract appreciably from the absorptive paper base used as the starting material and yet such as will enhance the wet strength of the base to a value many times that of the paper base used as the starting material. A paper so reinforced against the disintegrating action of water may be prepared by impregnating an absorptive paper base, for instance. a waterleaf paper base such as is customarily prepared for use as toweling, with a comparative dilute solution of cellulose ether, for instance, one of /2% to 2% cellulose ether content, squeezing the impregnated base to an ether content of about /2% to 2%, based on the dry weight of the paper base, and then precipitating the cellulose ether from solution in situ in the base. The impregnation with the dilute ether solution may be performed by passing the paper base through a bath of the other solution and the subsequent precipitation of the ether from solution may be performed by passing the impregnated base, squeezed to the desired ether content, through a bath of suitable precipitant solufinished paper sheet.

tion. If desired, suitable so-called wetting-out agents may be added to the ether solution or incorporated into the paper base to promote the influx of the solution into the paper base as well as to increase the rate of water influx into the The dried paper sheet of high absorbency and wet strength is serviceable to great advantage for such purposes as toweling, napkins, handkerchiefs, diapers, or the like. In preparing the cellulose ether solution of the desired dilution, it is necessary to use strongly alkaline water such as caustic soda solution of 5% to 6% strength in order to avoid premature and undesirable precipitation of the cellulose ether from solution. Accordingly, the originally prepared ether solution of about 8% cellulose ether content should be diluted with such a caustic soda solution to the desired cellulose ether content, say, /2% to 2% desired when producing papers possessed of both high wet strength and high absorbency, as hereinbefore described.

The reason why cellulose ethers of the kind herein described can be used successfully in producing absorbent papers of high wet strength is that they are not water-repellent as are cellulose derivatives of the nature of cellulose nitrate and cellulose acetate. On the contrary, they absorb water and are permeable to water to an appreciable extent, in fact, to as good if not better extent than cellulose regenerated from viscose. By limiting the amount of cellulose ether introduced uniformly throughout the paper base, only thin films of cellulose ether are deposited on the cellulose fiber constituting the paper base. These thin films are adequate for the purpose of integrating the fibers tenaciously against rupture by water and, by virtue of their thinness, water absorbency and water permeability, permit a ready diffusion of water not only into the pores and voids of the paper but also directly therethrough into the cellulose fibers themselves, wherefore the paper base treated with the cellulose ether is substantially as good a water imbiber and absorber as the waterleaf paper base used as the starting material. So far as I am aware, I am the first to recognize that the capabilities of cellulose ethers of the class herein described in absorbing water and in permitting water to difiuse therethrough can be put to play in making absorptive papers of high wet strength without running into those problems incident tothe use of viscose in the same connection.

Rather than introducing the cellulose ether substantially uniformly throughout a paper base, as hereinbefore described, in producing absorbent papers of high wet strength, it is possible to apply the ether solution locally, as along closely spaced criss-cross lines, to the paper. I regard this sort of practice, however, as being less desirable in that for the realization of a given overall wet strength in the paper, it is necessary to work with more concentrated ether solutions such as tend to obstruct locally the pores and interstices of the paper as well as to impart a non-uniform feel or harshness t0 the paper.

As already indicated, the papers of the present invention containing a hydroxy ether of cellulose may be advantageously treated to acquire increased softness, smoothness and pliancy. Such a treatment may be applied to papers of va rious characteristics made in accordance with the present invention. Thus, when the papers of the present invention are of high absorbency,

porosity and wet strength, they may be glyc- 18 erinated to good advantage to a glycerine content oi, say, up to about 15%. based on the dry weight of the paper, and thereby be put in a softer, smoother andmore pliant condition without impairment of their water-absorbing capabilities. To this end, they may be glycerinated with an aqueous solution of glycerine and thendried, such glycerination being accomplished either before or after the paper containing the precipitated hydroxy ether of cellulose has been dried. When glycerination is performed on the dried paper containing the precipitated hydroxy ether of cellulose, substantially anhydrous glycerine may be squeezed into the paper in the desired amount so as to avoid the necessity or redrying the paper. Other polyhydric alcohols, such as ethylene glycol, or solutions of watersoluble soaps, may take the place of glycerine, but I prefer to use glycerine because of its comparatively low cost and high effectiveness for the purpose in view.

I claim:-

1. Paper of high absorbency, porosity, and wet strength; containing a hydroxy ether of cellulose distributed substantially uniformly throughout its body only as thin films deposited on and integrating its fibers, said ether being present in such amount as not to detract appreciably from the porosity of the paper base.

2. Paper of high absorbency, porosity, and wet strength, containing a hydroxy alkyl ether of cellulose distributed substantially uniformly throughout its body only as thin films deposited on and integrating its fibers, said ether being present in such amount as not to detract appreciably from the porosity of the paper base.

3. Paper of high absorbency, porosity, and wet strength, containing the hydroxy ethyl ether of cellulose distributed in the amount of about to 2% substantially unitormly throughout its .body only as thin films deposited on and integrating its fibers. v

4. Glycerinated paper of high absorbency, porosity, and wet strength, containing a hydroxy alkyl ether of cellulose distributed substantially uniformly throughout its body only as thin films deposited on and integrating its fibers, said ether being present in such amount as not to detract appreciably from the porosity of the paper base.

5. A method of preparing absorptive paper products of high wet strength, which comprises preparing a solution of a hydroxy ether of cellulose'of about to 2% strength in an aqueous solution of caustic soda, impregnating an absorptive paper base substantially uniformly throughout its body with an excessive amount of such solution, removing'excess solution from the impregnated base to leave solution in such amount as to deposit only thin films of the ether ,on the fibers, and precipitating the other from solution as thin films on the fibers of substantially only the body of said base.

6. A method of preparing absorptive paper products. of high wet strength, which comprises preparing a dilute solution of a hydroxy alkyl ether of cellulose in an aqueous solution of caustic soda, impregnating an absorptive paper base substantially uniformly throughout its body with an excessive amount of such solution, removing excess solution from the impregnated base to leave solution in such amount as to deposit not more than about to 2% of the ether as thin films on the fibers, and precipitating the. ether from solution as thin films on the fibers of substantially only the body of said base.

GEORGE A. RICHTER.